The present invention relates to footwear, and in particular athletic and recreational footwear, e.g., running shoes, hiking shoes and sandals, used in conditions in which a variety of ground surfaces are typically encountered.
Modern athletic and recreational shoes typically comprise a highly refined combination of elements configured with the goal of optimally balancing, in light of the sport or activity for which the shoe is designed, the often competing concerns of cushioning, stability, durability and traction. The modern athletic or recreational shoe ordinarily has a multi-layer sole construction comprised of an outsole, a midsole and an insole. The outsole is normally formed of a durable material such as rubber to resist wearing of the sole during use. In many cases, the outsole includes lugs, cleats or other elements to enhance traction. The midsole ordinarily forms the middle layer of the sole and is typically composed of a soft foam material, e.g., foamed polyurethane or EVA, to cushion the impact forces experienced by the foot during athletic or recreational activities. In order to further enhance cushioning and reduce weight, it is known to incorporate within the midsole special cushioning elements, such as resilient fluid bladders, as taught in U.S. Pat. Nos. 4,183,156; 4,219,945; 4,340,626 to Rudy and 4,813,302 to Parker et al.
Recently, interest has grown considerably in lightweight athletic and recreational shoes specially configured for outdoor use. Lightweight materials and constructions developed for athletic shoes used primarily on level planar surfaces, e.g., running, basketball, baseball and tennis, have made their way into the hiking arena, replacing the traditional bulky, heavy and stiff leather hiking boot. This evolution, and the consequent availability of lightweight trail shoes, e.g., the NIKE Mada and Terra trail shoes, has spurred the growth of trail running as a sporting event and form of conditioning. The same technologies have been utilized to provide improved sandals, e.g., the NIKE Terra and Deschutz sandals, for use in wet and/or dry outdoor conditions, e.g., beach environments. In hiking, trail running, beach combing and other outdoor activities, a variety of ground conditions are likely to be encountered, vis, surfaces which are loose and firm, smooth and irregular, soft and hard, wet and dry, and inclined and level.
Athletic and recreational shoes of known types are not ideally suited for the wide variety of ground conditions that may be encountered in the aforementioned outdoor activities. Rather, to a significant degree, suitability for one type of ground condition has been achieved at the expense of suitability for other conditions. In particular, the soles of known athletic shoes generally do not provide an optimized balance of cushioning, stability and traction for diverse ground conditions. On one hand, a pattern of relatively deep, hard (stiff) outsole lugs, e.g., as provided in known hiking boots and trail shoes, is desirable to provide traction on soft, loose and/or irregular surfaces, but can result in less than ideal traction on smoother firmer surfaces. On the other hand, traction is enhanced on smooth and firm ground surfaces by softer sole elements which compress to increase the area of contact between the ground surface and the sole. Additionally, softer sole elements can afford greater stability and comfort due to their increased shock absorbing capabilities and ability to conform to small surface irregularities, e.g., small rocks. But, such relatively soft elements generally lack the aforementioned desirable traction characteristics of hard lugs.
The effectiveness of a mountain goat's hoof in providing that animal with sure footing on diverse and extreme ground conditions has been recognized. As described in the book entitled Beast the Color of Winter, the Mountain Goat Observed, by Douglas H. Chadwick, Sierra Club pub. (1983), "t!he sides of a mountain goat's toes consist of the same hard keratin found on the hoof of a horse or deer. Each of the two wrap around toenails can be used to catch and hold to a crack or tiny knob of rock. . . . The mountain goat is shod with a special traction pad which protrudes slightly past the nail. This pad has a rough textured surface that provides a considerable amount of extra friction on smooth rock and ice. Yet it is pliant enough for any irregularities in a stone substrate to become impressed in it and thereby add to the skidproofing effect."
The V-shape of the mountain goat's hoof has additional benefits that are illustrated by the following further description provided in the aforementioned book: "Make a wide V with your index and middle fingers and try pressing down against something with their tips. Since walking on an artiodactyl hoof is anatomically similar to walking on the tips of two fingers, the mountain goat feels the muscles and tendons working against each other somewhat the way you do. It adjusts the tensions accordingly in order to fine-tune its grip on uneven surfaces. . . . Now you will find that the more weight you put on your fingertips, the more they want to diverge sideways. In like fashion the mountain goat's toes divide the downward force of the weight on a hoof. When your fingers, or the toes of the hoof, are placed on an incline surface, part of the weight continues to be directed sideways--a horizontal vector of force as distinct from the vertical vector. There is thus less net force being exerted in a single downward line; hence there is less likelihood of overcoming the force of friction along that line and beginning to slide. . . . What is going on here is a fanning out of forces. If all the downward force could be converted into sideways forces, it would in effect be canceled out. . . . The third and final dimension is simpler to explain. Solid rock, talus, dirt or snow can become wedged in the crotch of the V and act as an additional brake."
To a limited degree, features from animal anatomies have been adapted for incorporation into shoe sole designs. Morrow et al. U.S. Pat. No. 4,769,931 discloses a cleated sole for footwear. The cleats are shaped and arranged in pairs to simulate animal hooves, primarily for the purpose of lessening noise and increasing traction for hunters. According to Morrow et al., a minimization of noise is achieved by limiting wearer contact with the ground. An absence of relatively soft (ground contact increasing) traction elements precludes the possibility of obtaining benefits in traction (as explained above) of the type attained by the mountain goat's soft hoof pads.
In contrast to the Morrow et al. patent, Gross et al. U.S. Pat. No. 5,367,791 discloses an athletic shoe sole construction wherein an insert is provided with relatively soft "tips." According to the patent, the tips are strategically located to absorb shock, add stability and reduce pronation. The tips do not appear configured to simulate an animal hoof in any way. Moreover, an absence of relatively hard traction elements, e.g., lugs, associated with the soft tips precludes benefits in traction similar to those that the mountain goat's toenails provide.